Can I render over painted brick or over old render?
Two backgrounds that render will not stick to on its own, the tests that tell you whether the surface is sound enough to work with, and the three ways to give it a key.
- Difficulty
- intermediate
- Time
- 12 min
- Read
- 4 min
Short answer
Not directly. Render bonds mechanically, and paint and old render both present a surface it cannot grip. Either remove the coating, or provide a key — a spatterdash coat, a proprietary bonding primer, or a mechanically fixed mesh or lath. The render is then only as good as what the paint or the old render is stuck to.
The question comes up because removing paint from brick or hacking off a whole elevation of old render is a large, unpleasant job and rendering over the top looks like a shortcut. Sometimes it can be done properly. The deciding factor is not whether render can be made to stick to the coating, but whether the coating is itself reliably stuck to the wall — because that is now the weakest link in the whole build-up.
Step by step
- Test the adhesion of what is already there.For paint, cut a cross-hatch with a knife and press strong tape over it, then pull. Paint that lifts is not a background. For render, tap the whole elevation systematically — hollow areas have debonded and must come off.
- Work out what the paint actually is.Sound modern masonry paint can sometimes be worked with. Flaking, chalky or multiple-layered paint cannot. Elastomeric and plastic coatings are the worst case — they are flexible and impermeable and render over them fails.
- Ask why the wall was painted or rendered in the first place.Frequently to cover poor or spalled brickwork, a previous damp problem, or a bad repair. Adding another layer over an unresolved problem hides it again rather than fixing it.
- Consider whether removal is genuinely the better route.On an old solid wall it usually is, because paint and cement render are often the reason the wall is damp. On a modern cavity wall with sound paint the calculation is different and rendering over may be reasonable.
- Provide a mechanical key if you proceed.Three routes. A spatterdash coat — a wet, coarse, thrown slurry of cement and sharp sand, left rough and allowed to cure — which is the traditional and most reliable answer. A proprietary bonding primer supplied as part of a render system. Or a stainless steel or glass fibre mesh mechanically fixed through to the masonry, which does not rely on the coating at all.
- Prefer the mechanical fix where there is any doubt.A mesh or lath fixed through the paint or the old render into sound masonry with stainless fixings takes the render's weight regardless of what the coating does. It is the belt-and-braces answer and it is what a competent contractor will propose on a doubtful background.
- Follow the system if you are using one.Monocouche and thin-coat manufacturers publish specific requirements for painted and rendered backgrounds, including which primers and which mesh, and the guarantee depends on following them.
- Think about vapour before you add a layer.Paint plus render on a solid wall is two barriers. If the wall was damp before, it will be damper after. On any pre-1919 solid wall, the honest answer is usually to remove rather than to add.
- Get the details reset.Adding render thickness changes every junction — sills, reveals, eaves, the damp proof course line, meter boxes, downpipe brackets. A bell cast bead at the base and stop beads at openings have to be worked out before you start, not improvised at the end.
- Take advice on anything listed or in a conservation area.Both rendering over brick and altering an existing finish can need consent, and on a listed building it certainly does.
Questions people ask
Will render stick to masonry paint?
Not reliably on its own. It needs a key — a spatterdash coat, a proprietary bonding primer, or a mechanically fixed mesh — and even then the whole system depends on the paint's own adhesion to the wall.
Can I render over old pebbledash?
If it is sound and well bonded, its rough texture is actually a good key, and a render can be applied over it after cleaning and priming. Tap it thoroughly first: pebbledash that rings hollow has to come off.
Is it cheaper to render over than to strip?
In labour, yes, considerably. In risk, no. Render applied over an unsound coating fails as a whole and takes the coating and often the face of the wall with it, and the second attempt costs more than doing it properly first.
Can I render over an old cement render on a solid wall?
You would be adding to a layer that may be the cause of the wall's problems. On a pre-1919 solid wall the usual right answer is to remove the cement render and use lime, not to render over it.